Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
NCTM or The Math Forum.


Math Forum
»
Discussions
»
sci.math.*
»
sci.math
Notice: We are no longer accepting new posts, but the forums will continue to be readable.
Topic:
A formal counterexample of Ax Ey P(x,y) > Ey Ax P(x,y)
Replies:
4
Last Post:
Dec 9, 2012 12:39 AM




Re: A formal counterexample of Ax Ey P(x,y) > Ey Ax P(x,y)
Posted:
Dec 8, 2012 6:30 PM


On Dec 9, 9:05 am, Dan Christensen <Dan_Christen...@sympatico.ca> wrote: > On Dec 8, 1:58 pm, Graham Cooper <grahamcoop...@gmail.com> wrote: > > > On Dec 8, 6:14 am, Dan Christensen <d...@dcproof.com> wrote: > > > > Let the domain of quantification be U = {x, y} for distinct x and y. > > > > Let P be the "is equal to" relation on U. > > > > Then Ax Ey P(x,y) would be true since x=x and y=y > > > > And Ey Ax P(x,y) would be false since no element of U would be equal > > > to every element of U. > > > > See formal proof (in DC Proof 2.0 format) athttp://dcproof.com/PopSci.htm > > > This is a classic Skolem Function example. > > This problem is central to predicate calculus. Like Russell's Paradox, > it has spurred various "solutions," Skolem functions being one of > them. My own DC Proof system is another, more natural one (IMHO). > > Dan > Download my DC Proof 2.0 software athttp://www.dcproof.com
a fine grain solution, but I think relational models, set at a time reasoning, although there is an intuitive understanding step required, will be more amenable to formal proofs being so much shorter and in the range of brute force proof search. 65 steps === n^65 is too big for a computer to ever come across, and that was a simple quantifier example.
Herc



